Kachina and Kiona, 4-year-old grizzly bears that live at the San Francisco Zoo, rush into their pen, curious about the wrapped packages placed strategically near the viewing glass.

Kiona grabs a giant candy cane that lies alluringly next to a fallen tree, while Kachina — the blonder of the two sisters — pounces on a colorful box until her paws reach the frozen fish, apples and honey hidden inside.

For the next 10 minutes, the bears are too busy to respond to calls from the bear keeper, Deb Cano, or to care that a crowd has gathered behind the glass.

The holiday season is officially declared at the San Francisco Zoo, where every weekend in December, polar bears, tigers, rhinos, meerkats and other residents will receive Christmas treats. The favorite foods of an array of animals are wrapped in colorful boxes by animal keepers and children, who are part of the zoo’s educational program. The presents are distributed on major holidays throughout the year to provide entertainment for visitors and enliven the animals’ pastime at the zoo.

“It’s fun to see your animal do something different,” said animal keeper Eva Mac, while gluing the wrapping paper with flour and water, a natural substitute for glue. “It’s something else to add to their lives.”

The keepers call this enrichment — adding something new to the animal’s environment to promote natural behaviors and keep the caged animals happier.

Thomas Night, who takes care of the meerkats, rabbits and turkeys, said enrichment varies for each animal. The resident hornbill, for example, gets the most joy out of ripping a phone book. While Cano likes to entertain her bears by skewering fruits on tree branches.

While Kachina and Kiona dig into their presents, on the other side of the zoo, a family of meerkats gets its holiday treats. As the animals watch curiously, Night puts a handful of mealworms inside a small box and stuffs it with straw. As he puts the box in their cave, the meerkats climb in one by one until the entire box rocks with excitement.

“You are giving them a project,” he explained. “The longer it takes, the sweeter the reward.”

This weekend, the zoo is giving out Christmas-themed gifts to polar bears and rhinos. Lions and meerkats get their treats next weekend, and South American bears and tigers receive theirs Dec. 22-23.